Printing plate and method of making the same



United States Patent 3,229,628 PRINTING PLATE AND METHOD OF MAKING THE SAME Elmore H. Mandel], Portage, Ind., and Kenneth L. Strachan, Glenview, 111., assignors to R. R. Donnelley & Sons (lompany, a corporation of Delaware No Drawing. Filed May 22, 1964, Ser. No. 369,604 2 Claims. (Cl. 101-1491) This invention relates to an offset plate made up of aluminum paper lamination and to a method of making such a plate. This application is a continuation-in-part of our application Serial No. 51,489, filed August 24, 1960, now abandoned, in the United States Patent Oflice.

According to the present invention, an offset plate is provided made up of a layer of aluminum bonded to water resistant paper. Printing areas are formed on the metal side of this plate by depositing thereon a heat setting ink insoluble in the offset ink to be used in printing with this laminated plate. The plate is next heated to cause the ink to set. The non-printing metal areas are thereafter made water receptive (desensitized), and the plate is then ready for immediate use in printing.

The plates of the present invention are characterized by a density such that on testing with an Ames caliper at 800 pounds per square inch, the compression of the plates will not exceed percent. This density is effected by using paper of the indicated density, and by avoiding the introduction of any heavy layer (1 mil or more) of adhesive between the metal and paper layers.

The heat setting ink is deposited on the plate by printing. Such printing does not effect any compression of the plate. Such embossing as may have been effected by letterpress printing is immediately ironed out when the plate is used in printing. In other words, the plate immediately (on the first impression) can produce good printing.

The aluminum layer of the plate is from 0.000015 to 0.00035 inch thick. This thickness is critical. At thickness values below the indicated lower limit, the aluminum tends to permit the migration of water into the underlying paper, which adversely affects the durability of the paper. At thickness values above the indicated upper limit, the plate is embossed when subjected to letterpress printing to form the image areas of the plate, and this embossing requires a number of impressions to be ironed out in the printing press. For instance, at a thickness of 0.00050 inch, impressions are needed to iron out the plate. At a thickness of 0.0035 inch, the plate must be put through a separate debossing operation before it is used for printing. In contrast, a plate having a metal thickness of 0.00035 inch can yield good printing on the first impression, as mentioned herein above.

The paper layer of the plate should be from 0.0025 to 0.010 inch thick. In plates used in small offset printing machines (plates 10 x 15 inches or smaller size), a paper thickness of 0.0035 inch is quite satisfactory, while for plates to be used in larger machines, a thickness of about 0.0045 to 0.0050 inch is preferred. The above indicated lower limit for paper thickness is set by the rigidity and strength required for easy handling of the plates without wrinkling and creasing. The above indicated upper limit for paper thickness is set by the fact that heavier paper tends to be excessively compressed or condensed on being subjected to letterpress printing. As mentioned herein above, there is an upper limit for the compressibility or density of the plates.

The paper can be made water resistant by any conventional method; for instance, treatment with 1 or 2% melamine resin or ureaformaldehyde resin. A number of water resistant or high wet strength papers are commercially available and can be used in the preparation ice of the plates of this invention. If desired, ordinary (rather than water resistant) paper can be used in making the paper-aluminum lamination, and then the paper is made water resistant after the lamination step has been carried out, as by application to the paper of any suitable varnish or the like.

When the thickness of the aluminum layer ranges from 0.00010 to 0.00035 inch, the plate is most suitably made by laminating paper and any of the commercially available aluminum foils having the indicated thickness. The composition of the aluminum may be that designated as 25 or 1145, which consists of 99.45% Al and 0.55% FeSi.

The foil surface should be free of the films believed by those skilled in the art to be necessary for satisfactory letterpress printing on oil, such as shellac, varnish and plastic films. Further the foil surface need not necessarily be grained.

The adhesive used for bonding the foil and paper together may be of any conventional thermo setting water resistant bonding agent suitable for that purpose; for instance, a heat settable casein adhesive. When Water forms part of the adhesive, such Water is driven off, through, or absorbed by the paper, which should then be made water resistant only after lamination has been done. The heat settable residue may be set (to render the film insoluble in water) by heating the laminate. A number of conventional compositions and methods are available for forming a water resistant bond between the foil and the paper.

When the thickness of the aluminum layer ranges from 0.000015 to 0.000050 inch, the plate is most suitably made by vacuum deposition of aluminum on paper. Any conventional vacuum deposition process may be employed for this purpose.

At an aluminum thickness of from 0.000050 to 0.00010 inch, the plates may be made either by vacuum deposition of aluminum or by bonding aluminum foil to paper.

The heat setting ink to be deposited by printing on the aluminum should yield (as disclosed hereinabove) a film insoluble in the offset ink employed when the plate is used for offset printing. Ordinarily, the heat setting ink should not dry merely by loss of solvent but should also change in chemical structure, as by polymerization, ester forma tion or oxidation. By way of an example, the commercially available varnishes containing pentaerythrolrosin esters and linseed or tung oil may be used, as may the conventional heat setting black letterpress inks containing an alkyd resin and a tung oil varnish. Many other conventional heat setting letterpress inks are also suitable, as will be apparent to those skilled in the art.

The heat setting ink may be deposited on the aluminum by rotogravure printing, offset printing or letterpress printing.

The term letterpress printing is used in this application in its broadest sense, to include all ink deposition by means of type or by means of relief engravings (line or halftone) in distinction to roto-gravure and offset printing. For our purposes, the type need not carry the ink. If desired, the ink may instead be carried by a ribbon (such as a typewriter ribbon), or by a sheet (such as carbon paper and the like) from which carrier (ribbon or sheet) the ink is transferred to the foil on impact of the type against the carrier supported by the foil. An example of such letterpress printing is given as follows.

The United States patents to Green Nos. 2,712,507 and 2,730,456 disclose pressure sensitive sheet materials containing microscopic pressure rupturable capsules. The heat setting letterpress inks referred to hereinabove may be enclosed in the capsules contained in such sheet materials, as by the methods disclosed in the United States patents to Green et al. Nos. 2,800,456 and 2,800,458. The

sheets including the ink containing capsules are placed on top of the aluminum layer of our offset plates, and letterpress printing is done by impacting type on the sheets, whereby the heat setting ink is transferred from the sheets onto the desired areas of the aluminum layer.

After the heat setting ink has been deposited on the metal side of our plate, the latter is heated to set the ink. For most inks a temperature of about 300 F., applied for from 3 to 10 minutes, will be sufficient, as is well known to those skilled in the art.

After the ink has been heat set, the areas not covered by ink must be treated to remove the oil film adhering to the aluminum to make these areas water receptive. For this purpose, the aluminum side of our plate may be swabbed with a strong solution of an anionic synthetic detergent, such as the commercially available sulfated fatty alcohol materials (Dreft), the alkyl aryl sulfonates (Tide), the sulfonic acid ester detergents (Whisk), and the like. Ordinary soap should not be used, nor the cationic and non-ionic detergents. Each area swabbed should be exposed to the detergent for, say, 10 to 15 seconds. After swabbing with detergent, the aluminum should be swabbed with water, to remove most of the detergent.

Preferably the oxide film on the aluminum should also be removed along with the oil film, as by immersing the plate in a 5% tri sodium phosphate solution at 150-160 F. for to 20 seconds, or until gas is evolved from the aluminum. Many conventional desensitizing methods are available for the same purpose.

The above noted oil and oxide films may be removed electrolytically, if desired. For this purpose, the plate is disposed on a fiat surface, and the aluminum is connected electrically to the cathode of a source of DC; for instance, a storage battery. The anode may be any suitable rigid metallic sheet resistant to anodic decomposition (such as aluminum), connected to the anode of a source of D.C., covered on one side by a layer of felt, polyurethane sponge or the like and provided on the other side with a handle. The felt or sponge is saturated with a suitable liquid electrolyte. This anode is moved around on the foil in the manner of a hand iron, to clean the whole foil surface. Devices suitable for use in such work are shown in US. Patent No. 2,833,702.

The liquid electrolyte may be any mildly alkaline water solution of a water soluble alkali metal base or salts of a weak acid, for instance, akali metal phosphates (e.g., dior trisodium phosphate), alkali metal carbonates (e.g., sodium carbonate or bicarbonate), and alkali metal hydroxide (e.g., sodium or potassium hydroxide). The concentration of the salt or base may be from 0.5 to 5 percent, say about 1 percent, or whatever concentration may effect a pH or about 8 to 10 or 11.

The electrolytic cleaning is suitably carried out at an electrode voltage of the order of magnitude of 6 volts and a low current density, say, on the order of 0.01 ampere per square inch. Each separate area to be cleaned may be exposed to contact with the anode carrying the electrolyte for a relatively short period of time, say, 10 seconds.

After the electrolytic treatment, the foil may be rinsed with water, to remove the electrolyte solution from the foil.

Other methods, known to those skilled in the art, are available for making the non-printing areas of our offset plate water receptive; for instance, the counteretching with acidic solutions commonly carried out before a photosensitive resist is applied to a grained aluminum plate.

After the non-printing areas have been made water receptive, our plate is ready for use in offset printing.

In offset printing with the plate of the present invention, any conventional offset ink may be used. Of course, care should be taken not to use any ink that will tend to dissolve or soften the ink forming the printing areas of our offset plates. This is well within the skill of those versed in the art.

When the plate is used in offset printing, the offset ink adheres to the areas having the deposit of heat set ink (which form discrete printing areas), but not to the water receptive areas. The adhering offset ink, on printing, is transferred to the offset blanket and therefrom to the paper being imprinted.

The preparation of a specific plate according to the present invention is described hereinbelow as an illustrative example of the product and methods of the present invention.

Aluminum foil 0.00035 inch thick is laminated to calendered kraft paper 0.0055 to 0.0060 inch thick by means of a film of conventional casein latex adhesive that is no more than about 1 mil in thickness, which is cured by heating the resulting laminate at about 275 F. for about 30 seconds. The water vaporized during this heating escapes through the paper. Thereafter, the paper is wa ter proofed by application of ordinary spar varnish in an amount of 0.007 pound per square foot. The varnished paper is allowed to air dry.

The printing image is applied by proofing on a letterpress proof press, using a letterpress form. The ink is a conventional black ink containing a pentaerythrol-resin ester and tung oil. The ink is thereafter heat set by heat ing the printed laminate at about 300 F. for a time up to 10 minutes, depending upon the amount of ink deposited on the foil.

The unprinted foil surface is thereafter rendered water receptive by cathodic treatment with a 1 percent solution of trisodium phosphate, using a cloth covered aluminum plate as an anode, at a current density of about 0.01 ampere per square inch, an electrode voltage of about 6 volts, and with each part of the foil area exposed to current for about 10 seconds. After the electrolytic treatment, the foil is rinsed or swabbed with water. The plate is then ready for use in offset printing.

The plates of the present invention represent a great advance in the art of offset printing, as will be evident from the following discussion.

Heretofore sheet metal plates have been the only kind available for offset printing in runs of 1000 to 1500 or more good impressions. These sheet metal plates cost upwardly of $1.00 per square foot and require complex processing (to prepare them for printing) and complicated lockups on the cylinders of the press.

Conventional paper plates may also be used for offset printing, but these paper plates cost from about 2.2 cents per square foot (good for up to impressions) up to 18 cents per square foot (good for up to about 1000 impressions).

The foil plates of the present invention cost about 2.25 cents per square foot and are good for 10,000 or 20,000 or 40,000 or more impressions. The vacuum deposited plates of the present invention cost about 1.75 cents per square foot and are good for 500 or more impressions. Additional savings may be realized in the extremely simple processing of the plates to prepare them for printing.

Thus, the present plate represents a very great cost saving and convenience to the offset printing art.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

We claim:

1. An offset printing plate comprising: a smooth surfaced aluminum foil layer having a thickness from about 0.00010 to about 0.00035 inch; a water resistant paper layer bonded to a surface of said aluminum by an intervening film of water resistant adhesive that is no more than about 1 mil in thickness, said paper having a thickness from 0.0025 to 0.010 inch; said aluminum layer providing a printing surface, and said plate having a compressibility such that the plate is not compressed more than ten percent when subjected to a pressure of 800 pounds per square inch.

2. A method of making a laminar printing plate with comprises: providing a Water resistant paper lamina having a thickness from about 0.0025 to about 0.010 inch and also having a compressibility such that the lamina is not compressed more than ten percent when subjected to a pressure of 800 pounds per square inch; and bonding to said paper lamina, by means of a film of water resistant adhesive having a thickness of no more than about 1 mil, a layer of aluminum foil having a thickness of about 0.00010 to about 0.00035 inch while maintaining the compressibility of the resulting laminated printing plate such that the plate is not compressed more than ten percent when subjected to a pressure of 800 pounds per square inch, said aluminum having a smooth printing surface.

References Cited by the Examiner UNITED STATES PATENTS 2,046,959 7/1936 Mehl 101-149.2 2,048,964 7/1936 Osborn 101149.2 2,119,031 5/1938 Wescott 101149.2 2,258,956 10/1941 Misuraca 101149.2 2,719,481 10/1955 Bothof et al. 101-149.2 2,760,432 8/1956 Wood 101149.2 3,016,824 1/1962 Ritzerfeld et al. 101-149.2

DAVID KLEIN, Primary Examiner. 

1. AN OFFSET PRINTING PLATE COMPRISING: A SMOOTH SURFACED ALUMINUM FOIL LAYER HAVING A THICKNESS FROM ABOUT 0.00010 TO ABOUT 0.00035 INCH; A WATER RESISTANT PAPER LAYER BONDED TO A SURFACE OF SAID ALUMINUM BY AN INTERVENING FILM OF WATER RESISTANT ADHESIVE THAT IS NO MORE THAN ABOUT 1 MIL IN THICKNESS, SAID PAPER HAVING A THICKNESS FROM 0.0025 TO 0.010 INCH; SAID ALUMINUM LAYER PROVIDING A PRINTING SURFACE, AND SAID PLATE HAVING A COMPRESSIBILITY SUCH THAT THE PLATE IS NOT COMPRESSED MORE THAN TEN PERCENT WHEN SUBJECTED TO A PRESSURE OF 800 POUNDS PER SQUARE INCH. 